The present invention is directed to new and improved diffusion transfer process photographic film units adapted to provide, as a function of the point-to-point degree of photoexposure, by diffusion transfer processing, a dye transfer image and to an improved light-sensitive silver halide emulsion and its utilization therewith.
Diffusion transfer photographic color systems generally depend upon the differential migration or mobility of a dye or dyes to provide color image formation. Differential dye mobility serves to define the resultant image of the system and is provided as a function of the development of exposed silver halide. For example, such differential mobility or solubility may be obtained by a redox reaction or coupling reaction. The image-wise distribution of the mobile dye material is selectively transferred, at least in part, by diffusion to a superposed or contiguous dyeable stratum to impart thereto the desired color transfer image.
Generally, multicolor images are obtained by employing a film unit containing at least two selectively sensitized silver halide emulsions each having associated therewith a dye image-providing material exhibiting desired spectral adsorbtion characteristics. Tripack structures usually are employed within the film units incorporating a blue-, a green-, and a red-sensitive silver halide layer having associated therewith, respectively, a yellow, a magenta and a cyan dye image-providing material.
The particular diffusion transfer system within which photosensitive silver halide layers are utilized may assume any of several diverse geometries and modes of image generating technique. For instance, one system as is described in U.S. Pat. No. 2,983,606 employs a photosensitive element comprising silver halide layers each of which is associated with a dye developer, a compound which is both a silver halide developing agent and a dye. Following exposure of the element it is developed by applying an aqueous alkaline processing composition thereto. The dye developer is oxidized in developed areas to provide an oxidation product which is appreciably less diffusible than the unoxidized dye developer. As a consequence, an imagewise differential distribution of diffusible dye developer may be transferred by diffusion to an image-receiving stratum which then carries the resultant positive dye transfer image. In one preferred system this image-receiving stratum or layer is superposed upon the photosensitive element subsequent to the exposure thereof and the processing composition is applied from a rupturable container forming part of the overall film unit. Following a suitable interval of imbibition permitting diffusion transfer, the resultant image is revealed by separation of the image-receiving element from the photosensitive element.
Other diffusion transfer systems have been introduced and proposed wherein the film unit is a composite structure of photosensitive element, reception layer and processing composition container. As disclosed in U.S. Pat. No. 3,672,890 a composite photosensitive structure, particularly adapted for reflection type photographic diffusion transfer color process employment, is shown to comprise a plurality of essential layers including, in sequence, a dimensionally stable layer preferably opaque to actinic radiation; one or more silver halide emulsion layers having associated therewith a diffusion transfer process dye image-providing material; a polymeric layer adapted to receive solubilized dye image-providing material diffusing thereto; and a dimensionally stable transparent layer. Following exposure to incident actinic radiation, the unit is processed by interposing, intermediate the silver halide emulsion layer and the reception layer, a processing composition including a light-reflecting agent.
The composite structure includes a rupturable container retaining the processing composition and the opacifying agent which is fixedly positioned along a transverse leading edge of the structure. Accordingly, upon removal of the unit from the camera, this rupturable container is subjected to an initial compressive pressure to effect the discharge of its contents intermediate the noted receiving layer and next adjacent silver halide emulsion.
The liquid processing composition, distributed intermediate the receiving layer and the silver halide emulsion, permeates the silver halide emulsion layers of the structure to initiate development of the latent images contained therein resultant from photoexposure. As a consequence of the development of the latent images, the diffusibility of dye image-providing material associated with each of the silver halide emulsion layers is controlled as a function of the point-to-point degree of the respective silver halide emulsion layers photoexposure. An imagewise distribution of mobile dye image-providing materials transfers by diffusion to the reception layer to provide the desired transfer dye image. Subsequent to substantial dye image formation in the image-receiving layer, means associated with the film unit structure are adapted to convert the pH of the film unit from a first processing pH at which the image dye-providing material is diffusible to a second pH at which such diffusion is substantially terminated and the transfer dye image exhibits increased stability. Preferably a sufficient portion of the alkaline ions of the processing composition transfer, by diffusion, to a polymeric neutralizing layer to effect reduction in the alkalinity of the composite film unit from a first alkaline processing pH to the second pH at which further dye image-providing material transfer is substantially obviated.
The transfer dye image may be viewed, as a reflection image, through the dimensionally stable transparent layer against a white background provided by the light-reflecting agent. This agent is distributed as a component of the processing composition intermediate the reception layer and next adjacent silver halide emulsion layer. The light-reflecting stratum serves to mask residual dye image-providing material retained in association with the developed silver halide emulsion layers subsequent to processing.
As disclosed in U.S. Pat. Nos. 3,615,421 and 3,661,585, the light-reflecting layer of the film unit may be initially disposed as a preformed processing composition permeable layer intermediate the reception layer and next adjacent silver halide layer in a concentration which prior to photoexposure is insufficient to prevent transmission therethrough of exposing actinic radiation and which, subsequent to processing, possesses a covering power effective to mask residual dye image-providing material retained associated with the developed silver halide emulsion layers. In U.S. Pat. No. 3,647,435, the light-reflecting layer of the film unit optionally may be initially formed in situ intermediate the reception layer and next adjacent silver halide layer during photographic processing of the film unit.
In U.S. Pat. No. 3,647,437, an opacifying system is disclosed comprising a light-absorbing reagent such as a dye which is present as an absorbing species at a first pH and which is converted to a substantially non-absorbing species at a second pH.
In U.S. Pat. No. 3,573,043, the polymeric neutralizing layer is disclosed to be optionally disposed intermediate the dimensionally stable opaque layer and next adjacent essential layer, i.e., the next adjacent silver halide/dye image-providing material component, to effect the designated modulation of the film unit's environmental pH. U.S. Pat. No. 3,576,625 discloses the employment of particulate acid distributed within the film unit to effect the modulation of the environmental pH. U.S. Pat. No. 3,573,044 discloses the employment of processing composition solvent vapor transmissive dimensionally stable layers to effect process modulation of dye transfer as a function of solvent concentration.
Another type of film unit may be constructed in accordance with the disclosure of U.S. Pat. Nos. 3,594,165 and 3,689,262. This composite photosensitive structure includes a transparent dimensionally stable layer carrying an image-receiving layer, a processing composition permeable light-reflecting layer, a photosensitive silver halide layer. The film unit further includes a separate dimensionally stable sheet element superposed on the surface of the photosensitive structure opposite the dimensionally stable layer as well as a rupturable container retaining processing composition for distribution of that processing composition intermediate the sheet and the photosensitive structure to effect processing.
Deriving an acceptable performance for color diffusion transfer film units has been found to rest upon a great number of factors. Such performance requires adequate speeds, optimization of the photoresponse gradiant traditionally represented by the curve shape of H and D type curves integrating color image density as a function of film unit photoexposure. Further, diffusion transfer processing must be operational over acceptably broad temperature ranges, must exhibit practical storage stability as well as exhibit an efficient and effective utilization of silver.
Extensive investigation has been conducted into both the basic content and particulate structures of silver halide emulsions utilized with photographic products. For diffusion transfer process film structures, such investigations are described, for instance in U.S. Pat. Nos. 3,697,269, 3,697,270 and 3,697,271. Those patents, as well as other publications, describe, inter alia, that optimized particulate silver halide distributions are desirably narrow in character, dysfunctions usually occuring where a particulate distribution extends into excessively fine sizes or excessively large grain structures. Generally, lower sensitivity is evidenced where excessively fine grain structures are encountered and unacceptable fog levels may be witnessed where a given distribution incorporates a too high proportion of grains of excessive size. Such narrow distributions have been obtained by fractionation techniques or by double jet silver halide preparation techniques, with, in some instances, blending of narrow fractions.